3d printing and measurement apparatus and method

ABSTRACT

A method of 3D printing an object includes receiving design information corresponding to an object for which a printed object is to be generated by a 3D printing operation according to a first set of print instructions, generating a plurality of measurement locations, printing successive layers which form the object, measuring the object at the measurement locations to form measurement data, comparing the measurement data with expected measurements of the measurement locations based on the design information, and generating, based on the comparing, deviation information. The measurement locations represent locations of the object to be measured by a measurement device. The deviation information represents deviations between the printed object following completion of the printing, and the object represented by the design information.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Patent Application No. 62/849,432, filed May 17, 2019, andtitled “Method and System For Improved Geometric Robustness of3D-Printed Parts,” the entirety of which is incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to an apparatus and method for accurately3D-printing and measuring a product.

BACKGROUND OF THE INVENTION

Industries have increasingly turned to 3D printing for manufacturingproducts such as system components. These 3D printers generally takedesign specification data as input, and employ an additive manufacturingtechnique to construct a finished product.

Due to limitations of 3D printing, conventional 3D printers have certainamounts of errors (e.g., imperfections) between the design specificationand the finished product.

Some conventional 3D printers address this limitation by employing anactive feedback process during the printing operation. The feedbackprocess identifies printing errors on already-printed portions of apartially-printed product, and adjusts the ongoing printing operationmoving forward to minimize errors in the remaining portions of theproduct being printed. This process is also known as in-processcorrection, and is employed to reduce imperfections on apartially-printed product. In general, using in-process correction mayprovide a printed product with sufficiently reduced imperfections to bedeemed acceptable to some recipients, without requiring a re-printing ofthe product.

However, the inventors of the present application recognized that forvarious industrial applications, it is critical that a component in asystem be manufactured precisely to design specifications. Not only mustthe dimensions of the component be accurate, the internal structure andcomposition must likewise be consistent with the specification.Deviations from specification could result in poor fitment ordurability, risking temporary system downtime from damage to that onesystem component, or even permanent damage to other system components,physical injury, or death.

The inventors of the present application recognized that for theseapplications, the level of imperfection reduction provided by in-processcorrection is not acceptable. By the time that an in-process correctionoperation identifies the need to perform the correction, thealready-printed portion of that product already contains a defect. As aresult of that existing defect, the entire product is deemed defectiveto the recipient. Moreover, in-process correction does not provideinformation as to the extent and location of imperfections within thefinished product. Nor does the process provide information that could beuseful towards a re-print operation of the product that resolves suchimperfections.

In other words, the inventors of the present application recognized thatthese conventional apparatuses seek to manufacture a product withreduced imperfections, rather than identifying the imperfections in analready-printed product and using such identifications to re-print aproduct that complies with design specifications and isimperfection-free.

Therefore, the inventors of the present application recognized that aneed exists in the art to accurately identify both external and internalimperfections in a printed product and utilize the imperfection data toconstruct a printing strategy that re-prints the product without theimperfections. The inventors of the present application also recognizedthat a need also exists in the art to incorporate a measurement device,such as a laser scanner, with a 3D printer so that such imperfectionsmay be identified and accurate correction information can be determinedfor constructing a re-print strategy. The inventors of the presentapplication recognized further that a need further exists in the art todetermine inaccuracies in the positioning of a printing system andprovide correction for such inaccuracies.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to an apparatus comprising aprocessor, and a memory, wherein the memory stores computer-readableinstructions which, when executed by the processor, cause the processorto: (i) receive design information corresponding to an object for whicha printed object is to be generated by a 3D printing operation accordingto a first set of print instructions, (ii) generate, using the designinformation, a set of measurement locations, the measurement locationsrepresenting locations on one or more surfaces of the object to bemeasured by a measurement device, (iii) generate a measurement strategyfor performing measurement of the set of measurement locations by themeasurement device, (iv) receive measurement data corresponding to themeasurement locations measured according to the measurement strategy,after the 3D printing operation according to the first set of printinstructions has been initiated on a print device, (v) compare themeasurement data to the design information, (vi) identify, based on thecomparing, deviations between the printed object and the objectrepresented by the design information, and (vii) generate informationcorresponding to the object which reflects the identified deviations.

In another aspect, the invention relates to a method of 3D printing anobject, comprising receiving design information corresponding to anobject for which a printed object is to be generated by a 3D printingoperation according to a first set of print instructions, generating aplurality of measurement locations, the measurement locationsrepresenting locations of the object to be measured by a measurementdevice, printing successive layers which form the object, measuring theobject at the measurement locations to form measurement data, comparingthe measurement data with expected measurements of the measurementlocations based on the design information, and generating, based on thecomparing, deviation information representing deviations between theprinted object following completion of the printing, and the objectrepresented by the design information.

In a further aspect, the invention relates to a method of manufacturingan object defined by design information, comprising controlling amanufacturing apparatus to manufacture the object according to a firstset of manufacturing instructions, controlling a measurement apparatusto measure the manufactured object, determining deviations between theobject as measured and the object as defined by design information, andgenerating a second set of manufacturing instructions according to thedetermined deviations.

In still a further aspect, the invention relates to a method ofcorrecting positioning errors in a system that includes a movementcomponent, comprising detecting a plurality of topographical featurespositioned at different locations on the surface of an object disposedwithin the movement system, comparing a location of the detectedtopographical features to expected locations for the topographicalfeatures, generating transformation information based on the comparison,and correcting movement instructions of the movement component based onthe generated transformation information.

In yet still a further aspect, the invention relates to a method ofcorrecting positioning error in a 3D-printing system that includes amovement component and a detection component, comprising detecting,using the detection component, a plurality of topographical featurespositioned at different locations on a reference object disposed on the3D-printing system, comparing a location of the detected topographicalfeatures to expected locations for the topographical features,generating transformation information based on the comparison; andcorrecting 3D-printing instructions for controlling the movementcomponent, based on the generated transformation information.

In again still a further aspect, the invention relates to a method ofmeasuring an object with a measurement apparatus that includes ameasurement component coupled to a movement component, comprisingmoving, with the movement component, the measurement component along ameasurement path in a forward direction, detecting, with the measurementcomponent, a forward measurement of the object along the measurementpath during the moving in the forward direction, moving, with themovement component, the measurement component along the measurement pathin a reverse direction opposite to the forward direction, detecting,with the measurement component, a reverse measurement of the objectalong the measurement path during the moving in the reverse direction,comparing the forward measurement and the reverse measurement, andgenerating a corrected measurement based on the comparing and at leastone of the forward measurement and the reverse measurement.

These and other aspects of the invention will become apparent from thefollowing disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate an apparatus, in accordance with oneembodiment.

FIG. 2 is a block diagram illustrating components of the apparatus, inaccordance with one embodiment.

FIG. 3 is a flow chart for performing 3D-printing and measuring anobject, in accordance with one embodiment.

FIG. 4 is a flow chart for performing 3D-printing and measuring anobject, in accordance with one embodiment.

FIG. 5 is a flow chart for performing 3D-printing and measuring anobject, in accordance with one embodiment.

FIGS. 6A and 6B are flow charts for performing 3D-printing and measuringan object, in accordance with one embodiment.

FIG. 7 illustrates a topographical example depicting sample points forprofile-scanning and edge-scanning measurements.

FIG. 8A illustrates an example of sample points for measurement on anobject, and FIG. 8B illustrates an example of remaining sample points onan object after a filter is applied.

FIG. 9A illustrates an example surface topology, FIG. 9B illustrates ascanning range of depths of the laser scanner, and FIG. 9C illustratesan example of an occluded region of a laser scanner.

FIGS. 10A and 10B illustrate overhead views of an edge and potentialedge scan directions.

FIG. 11 is a flow chart for performing 3D-printing and measuring anobject, in accordance with another embodiment.

FIG. 12 is a flow chart for performing 3D-printing and measuring anobject, in accordance with yet another embodiment.

FIG. 13 is a flow chart for performing 3D-printing and measuring anobject, in accordance with still another embodiment.

FIG. 14 illustrates a reference bed, in accordance with one embodiment.

FIG. 15 is a sectional view of a reference bed groove in accordance withone embodiment.

FIG. 16 is a flow chart for detecting gantry errors, in accordance withone embodiment.

FIG. 17 is a flow chart for detecting gantry errors, in accordance withone embodiment.

FIG. 18 is a sectional view of a reference bed groove and sample points,in accordance with one embodiment.

FIG. 19 is a flow chart for compensating for gantry errors, inaccordance with one embodiment.

FIG. 20 illustrates a phase shift experienced between forward andreverse scan signals.

FIG. 21 is a flow chart for detecting and compensating for backlashphase shift, in accordance with one embodiment.

FIG. 22 is a flow chart for detecting backlash phase shift, inaccordance with one embodiment.

FIG. 23 illustrates a representation of phase shift amounts orcompensation amounts based on location and scan direction.

FIG. 24 is a flow chart for compensating for backlash phase shift, inaccordance with one embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One aspect of the invention is an apparatus and method for performing3D-printing and scanning of an object.

FIGS. 1A-1B illustrate an apparatus 1000 in accordance with oneembodiment of the invention. The apparatus 1000 includes a controller 20and one or more print heads 10, 18. For instance, one head 10 maydeposit a metal or fiber reinforced composite filament 2, and anotherhead 18 may apply pure or neat matrix resin 18 a (thermoplastic orcuring). In the case of the filament 2 being a fiber reinforcedcomposite filament, such filament (also referred to herein as continuouscore reinforced filament) may be substantially void free and include apolymer or resin that coats, permeates or impregnates an internalcontinuous single core or multistrand core. It should be noted thatalthough the print head 18 is shown as an extrusion print head, “fillmaterial print head” 18 as used herein includes optical or UV curing,heat fusion or sintering, or “polyjet”, liquid, colloid, suspension orpowder jetting devices (not shown) for depositing fill material. It willalso be appreciated that a material bead formed by the filament 10 a maybe deposited as extruded thermoplastic or metal, deposited as continuousor semi-continuous fiber, solidified as photo or UV cured resin, orjetted as metal or binders mixed with plastics or metal, or arestructural, functional or coatings. The fiber reinforced compositefilament 2 (also referred to herein as continuous core reinforcedfilament) may be a push-pulpreg that is substantially void free andincludes a polymer or resin 4 that coats or impregnates an internalcontinuous single core or multistrand core 6. The apparatus includesheaters 715, 1806 to heat the print heads 10, 18, respectively so as tofacilitate deposition of layers of material to form the object 14 to beprinted. A cutter 8 controlled by the controller 20 may cut the filament2 during the deposition process in order to (i) form separate featuresand components on the structure as well as (ii) control thedirectionality or anisotropy of the deposited material and/or bondedranks in multiple sections and layers. As depicted, the cutter 8 is acutting blade associated with a backing plate 12 located at the nozzletoutlet. Other cutters include laser, high-pressure air or fluid, orshears. The apparatus 1000 may also include additional non-printing toolheads, such as for milling, SLS, etc.

The apparatus 1000 includes a gantry 1010 that supports the print heads10, 18. The gantry 1010 includes motors 116, 118 to move the print heads10, 18 along X and Y rails in the X and Y directions, respectively. Theapparatus 1000 also includes a build platen 16 (e.g., print bed) onwhich an object to be printed is formed. The height of the build platen16 is controlled by a motor 120 for Z direction adjustment. Although themovement of the apparatus has been described based on a Cartesianarrangement for relatively moving the print heads in three orthogonaltranslation directions, other arrangements are considered within thescope of, and expressly described by, a drive system or drive ormotorized drive that may relatively move a print head and a build platesupporting a 3D printed object in at least three degrees of freedom(i.e., in four or more degrees of freedom as well). For example, forthree degrees of freedom, a delta, parallel robot structure may usethree parallelogram arms connected to universal joints at the base,optionally to maintain an orientation of the print head (e.g., threemotorized degrees of freedom among the print head and build plate) or tochange the orientation of the print head (e.g., four or higher degreesof freedom among the print head and build plate). As another example,the print head may be mounted on a robotic arm having three, four, five,six, or higher degrees of freedom; and/or the build platform may rotate,translate in three dimensions, or be spun.

FIG. 1B depicts an embodiment of the apparatus 1000 applying thefilament 2 to build a structure. In one embodiment, the filament 2 is ametal filament for printing a metal object. In one embodiment, thefilament 2 is a fiber reinforced composite filament (also referred toherein as continuous core reinforced filament) may be a push-pulpregthat is substantially void free and includes a polymer or resin 4 thatcoats or impregnates an internal continuous single core or multistrandcore 6.

The filament 2 is fed through a nozzlet 10 a disposed at the end of theprint head 10, and heated to extrude the filament material for printing.In the case that the filament 2 is a fiber reinforced compositefilament, the filament 2 is heated to a controlled push-pultrusiontemperature selected for the matrix material to maintain a predeterminedviscosity, and/or a predetermined amount force of adhesion of bondedranks, and/or a surface finish. The push-pultrusion may be greater thanthe melting temperature of the polymer 4, less than a decompositiontemperature of the polymer 4 and less than either the melting ordecomposition temperature of the core 6.

After being heated in the nozzlet 10 a and having its materialsubstantially melted, the filament 2 is applied onto the build platen 16to build successive layers 14 to form a three dimensional structure. Oneor both of (i) the position and orientation of the build platen 16 or(ii) the position and orientation of the nozzlet 10 are controlled by acontroller 20 to deposit the filament 2 in the desired location anddirection. Position and orientation control mechanisms include gantrysystems, robotic arms, and/or H frames, any of these equipped withposition and/or displacement sensors to the controller 20 to monitor therelative position or velocity of nozzlet 10 a relative to the buildplaten 16 and/or the layers 14 of the object being constructed. Thecontroller 20 may use sensed X, Y, and/or Z positions and/ordisplacement or velocity vectors to control subsequent movements of thenozzlet 10 a or platen 16. The apparatus 1000 may include a laserscanner 15 to measure distance to the platen 16 or the layer 14,displacement transducers in any of three translation and/or threerotation axes, distance integrators, and/or accelerometers detecting aposition or movement of the nozzlet 10 a to the build platen 16. Thelaser scanner 15 may scan the section ahead of the nozzlet 10 a in orderto correct the Z height of the nozzlet 10 a, or the fill volumerequired, to match a desired deposition profile. This measurement mayalso be used to fill in voids detected in the object. The laser scanner15 may also measure the object after the filament is applied to confirmthe depth and position of the deposited bonded ranks. Distance from alip of the deposition head to the previous layer or build platen, or theheight of a bonded rank may be confirmed using an appropriate sensor.

Various 3D-printing aspects of the apparatus 1000 are described indetail in U.S. Patent Application Publication No. 2019/0009472, which isincorporated by reference herein in its entirety.

Laser Scanner

Various aspects of the laser scanner 15 will now be discussed. The laserscanner 15 may scan the section ahead of the next deposition in order tocorrect the Z height of the nozzlet 10 a, or the fill volume required,to match a desired deposition profile. This measurement may also be usedto fill in voids detected in the part. The laser scanner 15 may measurethe object after the filament is applied to confirm the depth andposition of the deposited bonded ranks. Distance from a lip of thedeposition head to the previous layer or build platen, or the height ofa bonded rank may be confirmed using an appropriate sensor, includingthe laser scanner 15.

The laser scanner 15 may be formed as a short-range laser scanner, ahigh resolution RGBD camera, a triangulating, time of flight, phasedifference, or interferometric scanner, a structured light camera orsensor, or the like. As illustrated in FIG. 2, the laser scanner 15includes a laser emitter 15 a and a laser receiver 15 b.

In one embodiment, the laser scanner 15 is mounted on (e.g., integralwith) the print head 10. In another embodiment, the laser scanner 15 ismounted on an independent head coupled to the print head 10. In yetanother embodiment, the laser scanner 15 is fixed to the apparatus 1000(e.g., mounted to a chassis), and the object to be measured is movedrelative to the laser scanner 15.

The laser emitter 15 a emits a laser beam of a predetermined sizedprofile on the surface of the object to be scanned. In one embodiment,the laser emitter 15 a is arranged such that the emitted laser beam isoriented generally downward at a predetermined angle relative to avertical direction of the apparatus. In one embodiment, thepredetermined angle is oblique. In one embodiment, the predeterminedangle is in a range between 0 and 89 degrees relative to the verticaldirection, preferably between 0 and 45 degrees, and even more preferablybetween 0 and 20 degrees.

In one embodiment, the predetermined angle of the emitted laser beam iszero, such that the laser beam is coincident with the vertical directionand oriented directly downward. In one embodiment, the laser beam is acircular (e.g., dot) profile. In one embodiment, the diameter of thelaser dot is between 0.1 and 100 μm, preferably between 20 and 80 μm,and even more preferably between 40 and 60 μm. In one embodiment, thelaser beam has a profile other than a circular profile, such as a lineprofile or a chevron profile.

The laser receiver 15 b senses the laser beam emitted from the laseremitter 15 a, incident and visible on a surface of the 3D-printedobject. In one embodiment, the laser receiver includes an optical sensor15 c and an optical system (not shown). In one embodiment, the opticalsensor 15 c is a two-dimensional sensor, including but not limited to aCCD or CMOS sensor. In another embodiment, the optical sensor 15 c is aline sensor. In one embodiment, the laser scanner 15 includes a visionsystem to analyze optical signals received from the optical sensor 15 c.

The optical sensor 15 c is arranged so as to face generally downward, ata predetermined angle relative to the vertical direction of theapparatus. In one embodiment, the predetermined angle is oblique. In oneembodiment, the predetermined angle is in a range between 0 and 89degrees relative to the vertical direction, preferably between 0 and 45degrees, and even more preferably between 0 and 20 degrees. In oneembodiment, the predetermined angle is zero, such that the opticaldetector is facing directly downward in the vertical direction.

In one embodiment, the laser beam emitted from the laser emitter 15 a isaimed directly downwards, and the optical sensor 15 c is likewise aimeddirectly downwards. In one embodiment, the laser beam emitted from thelaser emitter 15 a is aimed directly downwards, while the optical sensor15 c is oriented at an angle relative to the vertical direction,preferably in a range between 0 and 45 degrees relative to the verticaldirection, even more preferably between 0 and 20 degrees, and evenfurther more preferably between 0 and 5 degrees. In one embodiment, thelaser emitter 15 a and the laser receiver 15 b are arranged to be asclose to each other as possible.

The apparatus may rely on principles of triangulation to determine thedistance (e.g., depth) between the laser scanner 15 and the surface ofthe object on which the laser beam is incident. In particular, thedistance will affect the position of the laser beam as observed from thelaser receiver's perspective. The distance may be determined based onwhere the laser beam is observed within the laser receiver'sperspective.

It will be appreciated that laser scanning involves a line of sightbetween the laser emitter 15 a and the sample point being scanned (sothat the laser beam is incident on the sample point) and a line of sightbetween the optical sensor 15 c and the sample point (so that thevisualized laser beam incidence on the object is visible to the opticalsensor).

Laser Scan Modes

In one embodiment, the laser scanner 15 is operable in multiple modes ofscanning. In one embodiment, the laser scanner 15 is operable at leastin (i) a profile scan mode that performs a profile scan of a samplepoint, and (ii) an edge scan mode that performs an edge scan of a samplepoint. These modes of scanning are described as follows.

(i) Profile-Scanning

Profile-scanning of a sample point involves moving the print head 10(and therefore the laser scanner) to the X-Y position of a sample pointand taking a depth measurement to determine the Z position of the samplepoint on the surface of the scan object. The depth measurement may beperformed while the print head is stationary or while the print head iscontinuously moving. In many instances, profile-scanning of a samplepoint involves taking one depth measurement for that sample point whenscanning is performed in one direction along a scan path (unidirectionalscanning), or taking two depth measurements when scanning first in onedirection and then in the reverse direction along the scan path(bidirectional scanning). As a result, a profile scan provides arelatively rapid measurement of a sample point.

A profile scan provides a successful measurement when the sample pointis located on a surface that is relatively flat. However, depending oncharacteristics of the sample point, a profile scan may not produce asuccessful measurement, as described further below.

(ii) Edge-Scanning

For sample points where profile-scanning may not produce a successfulmeasurement, edge scanning may be used to measure the sample point. Inparticular, edge-scanning may produce a successful measurement when thesample point is located on (or near) an edge or on a surface with asteep slope, where a profile scan may not succeed.

Edge-scanning involves taking a series of measurements across the edgeof a part in order to determine the location of the edge and the depthof the sample point on (or near) that edge. Generally, an edge scanrequires taking multiple measurement readings per edge. The number ofmeasurements depends on various factors, such as desired tolerances andthe nature of the edge. In one embodiment, edge-scanning involvesapproximately 20-50 depth measurements per edge.

Once the depth measurements are obtained, the location and nature of theedge are determined. This may be accomplished using convolutionmethodologies of the edge scan signals to discriminate the edge. Afterthe edge has been identified, an accurate depth measurement may bedetermined in light of the nature of the edge.

Advantages of Profile-Scanning

For sample points where profile scanning is expected to be successful,profile scanning is generally preferred over edge scanning. This isbecause profile scanning is an order of magnitude faster than edgescanning, by requiring fewer depth measurements per sample point, asmaller scan path length, and less intensive computational processing.

Advantages of Edge-Scanning

While profile-scanning of a sample point is preferred when possible, itis recognized that profile scanning may only be suitable for certainsample points such as the top surface of a part. That is, profilescanning may encounter difficulties accurately determining the depthprofile at steeper points or at transitions (e.g., edges). As such, edgescanning is a preferable strategy for sample points which lie on steepwalls and underside surfaces, so that accurate depth measurements forthese sample points may be obtained.

FIG. 7 illustrates an example surface topology and a preferred scanningmode for various sample points. As shown, certain sample points (asidentified in FIG. 7) lie on a relatively flat surface, and thereforemay be profile-scanned to yield an accurate measurement. However, othersample points (as identified in FIG. 7) lie on a steep slope or along anedge, such that profile-scanning may not provide an accuratemeasurement. As a result, it may be preferable that these latter samplepoints are edge-scanned.

OTHER EMBODIMENTS

In one embodiment, the laser scanner 15 includes multiple laser emitters15 a and/or multiple laser receivers 15 b. In one embodiment, the laserscanner 15 includes multiple laser emitters 15 a per each laser receiver15 b, and/or multiple laser receivers 15 b per each laser emitter 15 a.

In one embodiment, the laser scanner 15 is positioned at locations otherthan above the object to be printed. In one embodiment, the laserscanner 15 is positioned to the side of the object to be printed. In oneembodiment, the laser scanner 15 is positioned below the object to beprinted.

In one embodiment, the apparatus 1000 includes multiple laser scanners15. In one embodiment, the apparatus 1000 includes multiple laserscanners 15 positioned at different perspectives (e.g., top, side,bottom) relative to the object.

In one embodiment, a touch probe is employed instead of (or in additionto) the laser scanner 15 to perform depth/distance measurements.

In one embodiment, the print nozzle is used instead of (or in additionto) the laser scanner 15 to perform a contact-sensing operation toperform depth/distance measurements. In particular, the apparatus 1000is equipped with detection capabilities for detecting when the nozzle 10(and/or nozzle 18) contacts the build platen 16, a print layer, and/or aprint material bead. By moving the nozzle 10 along the X, Y, and/or Zdirections and detecting when contact occurs between the nozzle 10 andthe print layer, the apparatus 1000 may take measurements of samplepoints on the print layer. For example, the nozzle 10 may be moved tothe X-Y position of the sample point and lowered until contact isdetected, and the Z-position at the time of contact is used to determinethe measurement.

In one embodiment, the laser scanner 15 is used to calibrate theZ-positioning within the apparatus 1000. A 3D printing system structuredto print form a deposition head capable of higher Z resolution (e.g.,beyond 200 micron layer height, to 100, 50, 25, or higher micron layerheight) encounters the problem of interference with, or excessiveclearance from, the build platen 16 in early layers. If the depositiontechnique is performed, e.g., less than 50 microns from the build platen16, one would expect the tolerance among the build platen surface andgantry supports (e.g., X, Y rails) to be sufficiently similar to the 50micron initial height such that no interference with the build platen16, or excessive clearance from the build platen 16, is encountered.

However, the 3D printing system includes tolerance stack-up andtemperature and environmental response. As different components of the3D printing system heat and cool (for example, the gantry beams,supports, and rails, or the build platen itself, or drive components),the distance between the deposition head's printing height and the buildplaten may vary, as may the nominal bead size etc. Accordingly, whilefactory-side calibration may be made versus systematic error among thecomponent parts, a calibration scan by the laser scanner 15 of the buildplaten 16, and potentially including a printed calibration target uponbuild platen 16, upon each print job is significantly more likely toaccount for additional environmentally determined systematic error.

With respect to the calibration target as a bead deposition, eachprinting material deposition head depicted in FIGS. 1A-1C, 28, 2A-2Htraces toolpaths, e.g., G-code and the like, to deposit printingmaterial, which may be in a line of minimum width and height (whether abead is deposited as extruded thermoplastic or metal, deposited ascontinuous or semi-continuous fiber, solidified as photo or UV curedresin, or jetted as metal or binders mixed with plastics or metal, orare structural, functional or coatings). The laser scanner 15 may bepositioned to measure surface profiles of the build platen 16 and/or aninitial bead. The surface profile may be a height map of the buildplaten, or of calibration beads or structures.

Optionally, the measured surface profiles of one, some, or manypreviously scanned build platens 16 and/or initial beads may be used ascalibration. A receiving circuit may receive the selection of buildplatens 16 and/or initial beads to be scanned from a remote process,from an external device, such as a local or remote computer performingslicing and providing the G-code, the identification, and the selection.

For the purpose of calibrating the printing deposition head and/or thelaser scanner 15 for a current environmental state, e.g., a “ready toprint” heated state of the system reflecting the effect of currentambient and machine temperature distribution on dimensions in thesystem, the controller 20 alternatively or further detects or receivesan indication the build platen 16 is to be scanned for calibrating thesystem, and/or receives a calibration target toolpath (e.g., from alocal or remote processor), and executes instructions to cause theprinting material deposition head that traces toolpaths to deposit aprinting material bead or shell to form a first layer 3D printedcalibration target (not shown, e.g., a straight line, a perimeter, aring, a square, a bar, a tower, or the like).

As noted, the controller 20 (which may include an inspection processorfor performing the inspection) may detect or receives an indication thebuild platen 16 is to be scanned for calibrating the system, and/orgenerate a calibration target toolpath for depositing the first layer 3Dprinted calibration target. Optionally, the target is printed in aportion of the build platen 16 that does not interfere with a part to beprinted using the calibration. The inspection processor may transmit thecalibration target toolpath defining the first layer 3D printedcalibration target for deposition by a 3D printer. After the 3D printerprints the calibration target, the inspection processor may compute aprocess calibration including a comparison between the received scannedsurface profile of the build platen 16 and/or the first layer 3D printedcalibration target and the calibration target toolpath. Similarly, theinspection processor may additionally, or in the alternative, receive atolerance definition for the build platen 16 and/or the first layer 3Dprinted calibration target, and may computing a process calibrationincluding toolpath adjustments for toolpaths based on the build platen16 surface profile, the first layer 3D printed calibration target, thetolerance, and the scanned surface profiles of the build platen 16and/or the first layer 3D printed calibration target. These processcalibrations and/or adjustments may be recorded as a current environmentcalibration adjustment in either or both of the 3D printer or theinspection processor and may be particularly suitable for calibrating(e.g., adjusting some actuations made by) the printing deposition headand associated actuators, including motors and heaters. For example,toolpath adjustments may correct or calibrate for an effect of at leastone of temperature, humidity or barometric pressure upon the printingmaterial or the 3D printer itself (including the build platen 16,supports, gantry, rails, frame, and/or actuator drive or guide surfacesor actuation amounts). Alternatively or in addition, the same or othertoolpath adjustments may correct or calibrate for an effect of at leastone of 3D printer component wear (e.g., loss of surface finish, wearingaway of contact surfaces), 3D printer component conditioning (e.g.,development of surface oxides, corrosion, roughening), or 3D printermaterial property variation (e.g., diameter, material properties, or thelike).

For example, in use, upon initiating a print job, the controller 20and/or its inspection processor may control the X, Y, and/or Z motors116, 118, 120 to raise the build platen 16 to a scanning height, andscan the build platen 16. The controller 20 and/or its inspectionprocessor may determine an average height of the build platen and set azero level, to which the initial printing layer may be referenced.However, if the build platen 16 height varies by, e.g., 150 microns,even if the zero level is set in the middle of the 150 micron range, fora printing height of 50 or 100 microns, some areas of the build platen16 may be too high and others may be too low.

Optionally, the controller 20 and/or its inspection processor maycontrol the laser scanner 15 moved together with the deposition head toscan the build platen 16 before, e.g., every print and calculate thecontour of a difference between the build platen 16 contour and the X-Ysupport contour, in the current conditions of temperature or otherenvironment. A reference plane or zero plane representative of the buildplaten 16 surface may be established, e.g., in the substantial center ofthe contour between the minimum and maximum build platen 16 surfaceheight difference (or, e.g., between high and low points using anotherstatistical reference such as a mean or median within +/−1, 2, or 3standard deviations of the samples of the difference contour). Usingthis difference contour, upon the first layer to be printed, wherever inthe X-Y motion of the deposition head the recorded difference contourindicates the build platen 16 is too low with respect to the (idealsurface) reference plane, the controller 20 and/or its inspectionprocessor may move the height of the build platen 16 up to compensate.Where the build platen 16 is high, the controller 20 and/or itsinspection processor may move the height of the build platen 16 down tocompensate. As this compensation is performed at each or any X-Yposition (or e.g., in zones), the deposition head deposits the firstlayer at the same height above the build platen 16.

Alternatively or in addition, to further compensate for deposition headvolume deposition rate or deposition shape, simultaneously or afterdetermining the difference contour, a calibration target bead may bedeposited on the build platen 16 and the height of the calibrationtarget bead from the build platen surface or difference contour scannedby the laser scanner 15. If the bead at the present, e.g., commandedvolume deposition rate is not the same as the first layer height, aconstant Z offset representing this bead size (e.g., for the firstlayer, or for many layers) may be used to print the layers (e.g., thedeposition height is alternatively or in addition compensated accordingto the current bead height).

In many forms of 3D printing, this compensation is most effective on thefirst and near-first layers. Accordingly, optionally, the compensationis progressively attenuated over several layers (e.g., over 10 layersand/or 1 mm) until the printer is depositing in a plane parallel to thereference or zero plane. Preferably, one or both of these compensationsare performed before every print job in order to detect and compensatefor minute changes in the difference contour due to the components ofthe printer expanding/cooling over time, or otherwise changing overtime, and compensate accordingly. As an additional benefit, the user canchange build platens, deposition heads, or other system components andthe same compensation will correct for variance.

In one exemplary process, the following steps may be performed beforeprinting to set the build platen 16 both level and determine thedifference contour.

(A) Heat or activate at least a portion of system components that mayundergo dimensional change when heated or activated (e.g., nozzles) orthat may heat other components of the printer in use. For example,deposition nozzles and/or build platen 16 may be pre-heated to operatingranges in this step.

(B) Scan the build platen 16 with the laser scanner 15 mounted to thedeposition head in a regular pattern, e.g., zigzag, boustrophedon, orother motion to find the “build platen height (e.g., print bed height)in a grid to form a 3D or X-Y-Z difference contour (which may cover onlya representative portion of the build platen 16, e.g., >¾ of the buildplaten 16.

(C) Calculate a best-fit or other statistical fit plane closest to thedifference contour or recorded heights and determine the differentialheight of the fit plane at each of multiple support locations (e.g., abuild platen 16 is generally supported at only 3 or 4 positions, ideallyin 3-point contact, of which 2 or 3 may have adjustable heights tochange the build platen 16 height). The fit plane may serve as thereference or zero plane.

(D) Calculate an average of the support locations, and provide acorrection of the support locations with respect to the fit plane, e.g.,as necessary, adjust at least one of the support locations so that all 3points are adjusted to the average of the support locations. If thisadjustment may not be made (e.g., because prior adjustments have movedthe support locations too far from nominal), each of the supportlocations may be set to some nominal value permitting full+/−adjustmentand the process begun again with the initial scan.

(E) Again scan the build platen 16 with the laser scanner 15 mounted tothe deposition head in a regular pattern, e.g., zigzag, boustrophedon,or other motion to find the X-Y-Z difference contour, and/or referenceplane.

Controller

The controller 20 controls the printing and laser scanning aspects ofthe apparatus 1000, including controlling the motors 116, 118, 120, theprint head(s) 10, 18, and the laser scanner 15. The controller 20operates the laser scanner 15 and collects data for measured surfaceprofiles. The surface profiles may be collected or transmitted during anongoing deposition, after part of a deposition, or after an entiredeposition, or any combination—following the printing head, orindependently of printing, or after the printing head has beendeactivated following the completion of a shell or layer.

The controller 20 may be formed as a single processor or a set ofmultiple processors. For instance, the controller 20 may be formed of acombination of a user interface controller, print control processor, animage processing processor, a laser scanner control processor, and/or ageneral processor. In one embodiment, all processors of the controller20 are locally provided in the apparatus 1000. In one embodiment, atleast one processor of the controller 20 is located remote from theapparatus 1000. The controller 20 is coupled to the memory 21, which mayinclude flash memory, RAM, and/or other volatile or non-volatile storageto store programs and active instructions for the controller 20 and datainvolved in operating the apparatus 1000.

The apparatus 1000 may further include an additional breakout board,which may include a separate microcontroller, that provides a userinterface and connectivity to the controller 20. The apparatus 1000 mayinclude an Ethernet controller that connects the controller 20 to alocal wired network and/or an 802.11 Wi-Fi transceiver that connects thecontroller 20 to a local wireless network. These controllers may alsoconnect the controller 20 to the Internet at large so as to send andreceive remote inputs, commands, and control parameters. The apparatus1000 may include a USB interface to connect the controller 20 toexternal peripherals or storage devices. The apparatus 1000 may includea touch screen display panel 128 to provide user feedback and acceptinputs, commands, and control parameters from the user. The apparatus1000 may include additional display(s), visual indicators (e.g., LEDs),and/or audio indicators (e.g., speaker) to indicate functionality and/orstatus to an operator, and may include additional input devices (e.g.,keyboard, mouse, trackpad, buttons) to receive input from an operator.

Scanning Measurement Operation

FIG. 3 illustrates an operation for performing 3D-printing and measuringan object and generating updated design data, according to oneembodiment.

First, in step S310, the controller 20 receives design data relating tothe object to be printed. For instance, the controller 20 may retrievethe design data and load the data into memory 21. The design data mayinclude information defining the geometry of the object to be printed.In one embodiment, the design data may be a computer-aided design (CAD)file.

In step S320, the controller 20 generates a first set of printinstructions based on the design data received in step S310. These printinstructions contain information for controlling the movement of thegantry 1010 and build platen 16, controlling the output of the printnozzlet 10 a, and controlling other components, for producing the objectto be printed. In one embodiment, the print instructions contain suchinformation on a print layer-by-layer basis.

In step S330, the controller 20 generates a set of sample points alongthe surface of the object as defined by the design data. The samplepoints are locations for performing a depth measurement. In oneembodiment, the controller 20 generates the sample points by performingrandom sampling of points on the object as defined by the design data.In another embodiment, the controller 20 generates the sample points byperforming a uniform sampling of points on the object as defined by thedesign data. In yet another embodiment, the controller 20 generates thesample points by performing the random or uniform sampling, and thenapplying a filter to the generated sample points to yield a desireddistribution of sample points. One example of performing step S330 isillustrated in FIG. 4 and described in detail below.

In optional step S335, the controller 20 receives input from an operatorof additional sample points on the surface of the object to add to theset of sample points generated in step S330. For instance, an operatormay desire that the operation particularly scrutinizes a specific pointor edge of interest on the object, and therefore may input such point oredge in the apparatus using one or more of the user interface inputsdescribed above. Nonetheless, it will be appreciated that this step isoptional, and in the event that the step is omitted, the operation mayproceed directly from step S330 to step S340.

In step S340, the controller 20 generates a scan strategy for conductingmeasurements during 3D-printing of the object, based on the samplepoints generated in step S330. The scan strategy may include one ormultiple elements. For instance, in the case that the laser scanner 15is operable in multiple modes (such as profile-scanning andedge-scanning), the controller 20 may determine an optimal mode toutilize for each sample point, and designate the optimal mode to thesample point. Additionally, the controller 20 may determine an optimallayer to perform the measurement of each sample point. Furthermore, thecontroller 20 may determine that the laser scanner 15 is not capable ofaccurately measuring one or more of the sample points. In this step, thecontroller 20 may also update the set of sample points, such as removingsample points from the set determined to be incapable of beingaccurately scanned by the laser scanner 15. One example of performingstep S340 is illustrated in FIG. 5 and described in detail below.

In step S350, the controller 20 initiates the 3D-printing operation ofthe object, setting the current layer to be printed as the bottom-mostprint layer. In step S351, the controller 20 causes the print head(s)10, 18 to print the current layer.

In step S352, the processor controller 20 determines, based on the setof sample points (as updated in step S340) and the scan strategygenerated in step S340, the sample point(s) to be measured at thecurrent layer. For each of these sample point(s), the controller 20directs the laser scanner 15 to measure the sample point according tothe scan strategy. For instance, where the scan strategy has designatedthat the sample point should be measured using a profile scan, thecontroller 20 directs the laser scanner 15 to measure the sample pointusing profile-scanning. And where the scan strategy has designated thatthe sample point should be measured using an edge scan, the controller20 directs the laser scanner 15 to measure the sample point usingedge-scanning. The controller 20 stores the results of the scan in thememory 21.

In step S353, the controller 20 determines whether another print layerremains to be printed for the object. If another print layer remains tobe printed, the operation proceeds to step S354. If the current printlayer is the final print layer, the operation proceeds to step S360.

In step S354, the controller 20 increments the current print layer tothe next layer, thereby advancing to the next layer. Generally, the nextlayer is the successive layer upwards in height. The operation thenreturns to step S351.

In step S360, the controller 20 compares the measurement data stored foreach of the sample points in the set, with expected data based on thegeometry information in the design data. This comparison identifies thedefects in geometry within the actual printed object relative to thespecified geometry of the object as defined by the design data. In oneembodiment, the controller 20 applies surface modeling methodologies tothe design data, to determine the expected distance for each samplepoint.

In step S370, the controller 20 generates updated design data based onthe design data and the results of the comparison from step S360. Forexample, the controller 20 may generate a transformation matrix definingthe change from the expected data to the actual measured data for one ormore sample points. The controller 20 may then apply the inverse of thattransformation matrix to the design data, to generate the updated designdata. In one embodiment, the controller 20 may compute more complex andsophisticated transformations based on the expected data and the actualmeasured data, to generate the updated design data. Since the updateddesign data is modified in light of the comparisons from step S360, itis expected that printing of the updated design data will produce anobject with fewer geometry defects as compared to the current printedobject that was measured.

It will be appreciated that in one embodiment, for profile-scanningand/or edge-scanning, the apparatus 1000 may perform a set ofmeasurements across multiple layers in a single pass, rather thandiscriminating sample points strictly on a layer-by-layer basis.

FIG. 4 illustrates one example of steps that may be employed to performstep S330 of generating a sample point set. In step S400, the controller20 generates an initial pool of sample points. This sample pointgeneration may be accomplished using a variety of known approaches, suchas random sampling or uniform sampling of points on the surface of theobject as defined by the design data. FIG. 8A illustrates an example ofsample points (depicted as dots) that may be generated across thesurface of an object to be printed. In one embodiment, the number ofgenerated sample points in the initial pool is at least 2.5 times amaximum desired number of final sample points.

In step S410, the controller 20 applies a filter to the initial pool ofsample points. The filter removes certain sample points from the pool,such that the final pool contains sample points that are distributed ina desired pattern. The particular filter to be applied will depend onthe specific desired distribution, which in turn depends on individualpreferences and priorities. For example, the filter may update theinitial pool such that the final sample points are evenly distributedacross the object. Or, the filter may update the initial pool such thatcertain areas of the object have a greater density of sample points.FIG. 8B illustrates an example of sample points remaining from the FIG.8A example, following an application of a filter that produces an evendistribution of sample points.

In step S420, the controller 20 stores, in the memory 21, the final poolof sample points as the set of sample points to be measured.

It will be appreciated that the steps illustrated in FIG. 4 is merelyone example of performing step S330, and that any known approach togenerating a sample point set may be used to perform step S330.

FIG. 5 illustrates one example of steps that may be employed to performstep S340 of generating a scan strategy and updating the sample pointset. In step S500, the controller 20 determines which sample points, ofthe set of sample points, will be measured using a profile scan. Thecontroller 20 also generates an initial scan strategy that includesinformation for profile-scanning these sample points. One example ofperforming step S500 is illustrated in FIG. 6A and described in detailbelow.

In step S540, the controller 20 determines which sample points, of theremaining sample points in the set that will not be profile-scanned,will be measured using an edge scan. The controller 20 also updates thescan strategy to include information for edge-scanning these samplepoints. One example of performing step S540 is illustrated in FIG. 6Band described in detail below.

In step S570, the controller 20 discards the remaining sample pointsfrom the set that have not been designated for profile-scanning in stepS500 or edge-scanning in step S540. These sample points have beendetermined as being incapable of being successfully measured by thelaser scanner 15.

It will be understood that the laser scanner 15 may have additionalmodes, or the apparatus 1000 may have additional components in additionto the laser scanner 15 for measuring the object. Therefore, it will beappreciated that step S340 may be modified to accommodate these modes orcomponents, and to generate a scan strategy that incorporates samplepoint measurement based on these modes or components, without deviatingfrom the invention.

FIG. 6A illustrates one example of steps that may be employed to performstep S500 of determining the sample points to be measured usingprofile-scanning and generating a scan strategy. As described above,profile-scanning is generally preferred over edge-scanning, but isgenerally limited to sample points which lie on a relatively flatsurface and are not located near an edge. For instance, profile-scanningmay not provide an accurate measurement if the sample point is shadowedby a ridge, which can occur if the sample point is in a depression(e.g., indentation or hole) relative to its surrounding surface.

In step S511, the controller 20 generates an initial candidate pool ofsample points being considered for profile-scanning. In one embodiment,the initial candidate pool is simply the set of sample points generatedin step S330, as profile-scanning is a preferred scan mode based on itsscan speed relative to edge-scanning.

In step S512, the controller 20 discards, from the candidate pool,sample points which lie on a slope steeper than a threshold slope. Asdescribed above, profile-scanning may not be capable of accuratelymeasuring sample points on steep slopes. Therefore, these sample pointsmay preferably be excluded from profile-scanning. The controller 20 mayperform step S512 by calculating the slope of the surface on which eachsample point in the candidate pool is located. The slope may becalculated based on, for example, surface modeling of the object asdefined by the design data. The controller 20 may then compare eachcalculated slope with a threshold slope, and remove sample points fromthe candidate pool for which the corresponding calculated slope exceedsthe threshold slope. In one embodiment, the specific threshold slope ispredetermined based on various conditions, such as the limitations ofthe laser scanner 15, the desired confidence of profile-scanningmeasurement accuracy, and the nature of the deposition print material.

In step S513, the controller 20 discards, from the candidate pool,sample points having exposed roof regions smaller than a threshold. Inone embodiment, the threshold is predetermined based at least on thespot size of the laser beam emitted by the laser emitter. Excessivelysmall exposed roof regions prevent the emitted laser beam incident onthe sample point from being useful and sufficiently detectable by thelaser receiver 15 b. Therefore, these sample points may preferably beexcluded from profile-scanning. FIG. 9A illustrates an example of atopology and how the slope θ and the width of the exposed roof region(“land”) on the topology influences the ability of the laser scanner 15to profile-scan a location. If the slope θ is excessive or the land isinadequate, the laser beam spot from the laser scanner 15 may not beincident on the topology surface in a manner that can accurately reflectthe depth from a scan of that location.

In step S514, the controller 20 establishes a scan strategy thatdesignates the remaining sample points in the candidate pool forprofile-scanning. The scan strategy contains information pertaining toperforming measurements of the object, such as the sample points to bemeasured, the mode in which each sample point will be measured, and theprint layer during which each measurement will be performed. That is,the scan strategy will be employed during the scanning and printingoperation to dictate the manner of measuring the object being printed.

In step S520, the controller 20 determines, for each print layer, whichof the sample points below that layer are visible to the laser receiver.For instance, as illustrated in FIG. 9B, when the laser emitter 15 a andthe laser receiver 15 b of the laser scanner 15 are spaced a distance Lnfrom each other, the laser scanner 15 may possess a scanning depth rangefrom layer i (at a distance of Lv from the laser scanner 15) down tolayer j, based on angles θ₁ and θ₂. This scanning range provides theability for the laser scanner 15 to, when scanning sample points onlayer i, possibly also scanning other sample points down to layer j.However, as illustrated in FIG. 9C, higher layers may form overhangswhich occlude portions of a lower layer, preventing sample points onthose occluded portions to be measured once the overhang is formed.Therefore, such determination in this step is useful to ensure thatmeasurement of such occluded sample points is performed prior toformation of the layer containing the overhang.

In step S521, the controller 20 determines an optimal approach toconducting the overall operation of profile-scanning the sample pointsso designated. The optimal approach may include the order and timing forprofile-scanning the designated sample points, where the timing mayinclude the optimal print layer from which to conduct the profile scan.The processor may incorporate one of various methodologies relating tosolving a set cover problem. The precise methodology and optimizationmay depend on desired objectives and their relative importance. Variousobjectives may include whether scans should preferably be conducted ateven intervals, whether scans should preferably be conducted in as fewlayers as possible, whether scans should preferably be conductedmultiple times or from multiple layers, etc.

In step S522, the controller 20 updates the scan strategy to assign, foreach sample point that has been designated for profile-scanning, theprint layer for performing the profile-scanning. In particular, thecontroller 20 processes the optimal approach determined in step S521 toextract the optimal print layer to perform the measurement of eachsample point designated for profile-scanning, and incorporates thisinformation into the scan strategy. Optionally, the controller 20 mayalso update the scan strategy to include a scan path for each printlayer that will be traversed so as to pass over the relevant samplepoints for that layer.

FIG. 6B illustrates one example of steps that may be employed to performstep S540 of determining the sample points to be measured usingedge-scanning and updating the scan strategy. In step S541, thecontroller 20 generates an initial candidate pool of sample points beingconsidered for edge-scanning. In one embodiment, the initial candidatepool simply consists of the remaining sample points in the sample pointset that have not already been designated for profile-scanning.

In step S542, the controller 20 discards, from the candidate pool,sample points for which no scan path exists for performing the edgescan. That is, the controller 20 determines that the nature of the edge(e.g., its geometry or profile) renders edge-scanning ineffective. Thismay occur for example, if the edge is located on a narrow sliver ofmaterial, is proximate to other edges, or has a unique profile thatprevents edge-scanning

In step S543, the controller 20 updates the scan strategy to designatethe remaining sample points in the candidate pool for edge-scanning.

In step S544, the controller 20 determines, for each sample pointdesignated for edge-scanning, an optimal scan path for performing theedge scan. For instance, FIG. 10A illustrates an overhead view of anexample edge and two potential scan paths for performing an edge scan ofthe edge in different directions, while also illustrating the scansignals that are produced by such scan paths. In one embodiment, thedetermination of the optimal scan path involves the determination of theoptimal length of the scan path. For instance, a shorter scan pathlength may reduce the time needed to perform the edge scan, but mayyield insufficient measurement data in which to discriminate the edge.In one embodiment, the determination of the optimal scan path involvesthe determination of the optimal angle relative to the edge. Forinstance, FIG. 10B illustrates an overhead view of potential scan pathangles 0 through 4 from which an optimal angle may be selected. It willbe appreciated that the specific optimization methodology fordetermining optimal scan paths may depend on various objectives andtheir relative importance, such as the desired scan speed, thelimitations of the laser scanner, the desired confidence of edge-scanmeasurement accuracy, and the nature of the deposition print material.

In step S545, the controller 20 determines an optimal approach toconducting the overall operation of edge-scanning the sample points sodesignated. The optimal approach may include the order and timing foredge-scanning the designated sample points, where the timing may includethe optimal print layer from which to conduct the edge scan. This stepmay incorporate the same or similar methodology as step S521 describedabove for profile-scanning. That is, the processor may incorporate oneof various methodologies relating to solving a set cover problem, wherethe precise methodology and optimization may depend on desiredobjectives and their relative importance. Various objectives may includewhether scans should preferably be conducted at even intervals, whetherscans should preferably be conducted in as few layers as possible,whether scans should preferably be conducted multiple times or frommultiple layers, etc. The controller 20 may also incorporate theexisting scan strategy formulated for profile-scanning into itsoptimization analysis.

In step S546, the controller 20 updates the scan strategy to assign, foreach designated sample point, (i) the optimal scan path for the samplepoint determined in step S544, and (ii) the print layer foredge-scanning the sample point based on the optimal approach determinedin step S545.

FIG. 11 illustrates an operation for performing 3D-printing andmeasuring an object and generating updated print instructions, accordingto another embodiment. The FIG. 11 embodiment differs from the FIG. 3embodiment in that the comparison information between the measurementdata and the design data is used to generate updated print instructionsrather than updated design data. As a result, step S370 in FIG. 3 hasbeen replaced with step S370 a in FIG. 11. It will be appreciated thatthe same reference numerals utilized in FIG. 3 are again utilized inFIG. 11 to denote the same steps.

In step S370 a, the controller 20 generates updated print instructionsbased on the first set of print instructions and the results of thecomparison from step S360. For example, the controller 20 may generate atransformation matrix defining the change from the expected data to theactual measured data for one or more sample points. The controller 20may then apply the inverse of that transformation matrix to the firstset of print instructions, to generate the updated print instructions.In one embodiment, the controller 20 may compute more complex andsophisticated transformations based on the expected data and the actualmeasured data, to generate the updated print instructions. Since theupdated print instructions are modified in light of the comparisons fromstep S360, it is expected that printing based on the updated printinstructions will produce an object with fewer geometry defects ascompared to the current printed object that was measured.

FIG. 12 illustrates an operation for performing 3D-printing andmeasuring an object and generating updated design data, according to yetanother embodiment. The FIG. 11 embodiment differs from the FIG. 3embodiment in that the measuring of the sample points is performed onlyafter the object has been fully printed, rather than being performedduring the printing operation. As a result, step S340 in FIG. 3 has beenreplaced with step S340 a in FIG. 12, step S351 in FIG. 3 has beenomitted, and step S355 has been added.

In step S340 a, the controller 20 generates a scan strategy forperforming measurements after the object has already been 3D-printed,based on the sample points generated in step S330. The scan strategy mayinclude one or multiple elements. For instance, in the case that thelaser scanner 15 is operable in multiple modes (such as profile-scanningand edge-scanning), the controller 20 may determine an optimal mode toutilize for each sample point, and designate the optimal mode to thesample point. Furthermore, the controller 20 may determine that thelaser scanner 15 is not capable of accurately measuring one or more ofthe sample points. In this step, the controller 20 may also update theset of sample points, such as removing sample points from the setdetermined to be incapable of being accurately scanned by the laserscanner 15.

In step S355, the controller 20 directs the laser scanner 15 to measureeach of the sample points in the set according to the scan strategy. Forinstance, where the scan strategy has designated that the sample pointshould be measured using a profile scan, the controller 20 directs thelaser scanner 15 to measure the sample point using a profile scan. Andwhere the scan strategy has designated that the sample point should bemeasured using an edge scan, the controller 20 directs the laser scanner15 to measure the sample point using an edge scan. The controller 20stores the results of the scans in the memory 21.

FIG. 13 illustrates an operation for performing 3D-printing andmeasuring an object and generating updated print instructions, accordingto still yet another embodiment. The FIG. 13 embodiment differs from theFIG. 3 embodiment by incorporating both the unique aspects of the FIG.11 embodiment and those of the FIG. 12 embodiment, in that (i) thecomparison information between the measurement data and the design datais used to generate updated print instructions rather than updateddesign data, and (ii) the measuring of the sample points is performedonly after the object has been fully printed, rather than beingperformed during the printing operation.

While the above operations have been described based on a singlemeasuring and printing of an object to generate updated design data orprint instructions, in one embodiment, the operation may utilize aniterative approach involving multiple repeated measurements andre-printings of objects. In such an approach, each successive re-printideally produces a printed product increasingly closer to the intendeddesign (as defined by the original design data).

In yet another embodiment, the apparatus performs in-process correctionin combination with the measurement operations, to preemptively correctprinting defects during printing to minimize defects in the remainingportion of the object being printed. While such an approach stillresults in a certain extent of printing defects (which may still renderthe printed object unacceptable), this approach may reduce the totalextent of printing defects required to be corrected. As a result, bycombining in-process correction with corrections based on the samplepoint measurement operation, an acceptable object re-print may beachievable with an ultimately fewer number of re-prints.

In still another embodiment, the apparatus takes the measurements at allX-Y points (or at X-Y points spaced at certain intervals), for all printlayers. With such an approach, the controller 20 may use the measurementdata to construct a full three-dimensional model of the printed object.The full three-dimensional model may include geometries definingreference layers, walls, infill (e.g. triangular, hexagonal), etc.

While the above operations have been described with respect to the laserscanner 15, it will be appreciated that the invention encompasses theuse of other measurement approaches. For instance, in one embodiment,the apparatus 1000 includes a camera for imaging every print layer andreconstructing a three-dimensional model from the image data.

In one embodiment, the apparatus 1000 is incorporated with athree-dimensional measurement component such as an X-ray computedtomography (CT) device to perform the measurements during printing. Forinstance, the apparatus 1000 may be placed within an X-ray CT machine toperform the measurements.

In one embodiment, the partial or fully-complete printed object isplaced in a non-destructive measurement device to perform themeasurements. In one embodiment, the partial or fully-complete printedobject is placed in an X-ray CT device to perform the measurements.

Gantry Error Detection and Compensation

Another aspect of the invention is an apparatus and method for detectingand compensating for gantry positioning errors. It will be appreciatedthat this aspect may be used in combination with the above-describedapparatuses and methods of performing 3D-printing and scanning of anobject and the below-described apparatuses and methods for detecting andcompensating for backlash.

One problem that may arise with movement systems, such as a gantry withan X rail and a Y rail, is that the actual positioning of a movementhead does not precisely correspond to the intended positioning inputs.For instance, if the X rail and Y rail of the gantry 1010 are notprecisely aligned at 90 degrees with respect to each other, the gantry'sX-Y coordinate system will be skewed relative to a true X-Y coordinatesystem. Additional low-order positioning deviations such as rotation,translation, and scale, could also exist between these coordinatesystems. Furthermore, higher-order and/or localized positioningdeviations could also exist between these coordinate systems, such asbowed gantry rails and/or backlash.

Such gantry deviations may influence both the measurement and printingoperations described above, resulting in inaccuracies in both thescanning process and the printed object. Therefore, a need exists in theart to detect such gantry deviations as gantry errors and compensate forsuch errors, so that the apparatus may perform accurate measurement andprinting operations.

One aspect of the present invention includes a reference bed that isinstalled on the apparatus, and an operation for detecting features onthe reference bed to determine gantry errors. The present invention alsoincorporates an operation for compensating for the detected gantryerrors during normal operation of the apparatus.

FIG. 14 illustrates a reference bed 1400 that may be used in combinationwith an operation for detecting gantry errors. In one embodiment, thereference bed 1400 includes mounting hardware, such as bolts, that iscompatible with mounting hardware of the build platen 16 of theapparatus 1000. As such, the reference bed may be attached to theapparatus 1000 in place of the print head when performing an operationto detect gantry errors. In one embodiment, the reference bed 1400 hasthe same thickness, general shape, and/or weight as the build platen 16.

The reference bed 1400 includes a plurality of grooves on its surface.In one embodiment, the grooves are arranged in a grid pattern, includingboth grooves 1410 running along the horizontal (X) direction and grooves1420 running along the vertical (Y) direction. In one embodiment, thegrooves running along each direction are spaced at equal intervals fromone another.

FIG. 15 illustrates, in a sectional view, the profile of one example ofa groove on the reference bed 1400. In one embodiment, the profile ofeach groove includes a left slope 1500 and a right slope 1510intersecting at a center point 1520, thereby forming a V-shape into atop surface 1530 of the reference bed. In one embodiment, the left slope1500 and the right slope 1510 are symmetrical, and the center point 1520reflects the center of the groove. It will be appreciated that thespecific number of grooves, groove depths and widths, and intervalsbetween grooves may be selected based on various design considerations.

In one embodiment, the grooves are manufactured so as to be sufficientlystraight and evenly spaced, such that the centers of the grooveintersections form a sufficiently square grid. While it will beappreciated that realistic manufacturing limitations prevent anabsolutely “perfect” groove, the reference bed 1400 and its grooves arestill preferably manufactured with at least sufficiently closetolerances which exceed the measurement resolution of the laser scanner15. That is, the grooves are “perfectly” straight and evenly spaced fromthe perspective of the laser scanner's ability to detect them.

In one embodiment, the reference bed 1400 is formed of a material with alow coefficient of thermal expansion. In one embodiment, the referencebed 1400 is formed of aluminum. In one embodiment, the reference bed1400 is formed of a material with a known coefficient of thermalexpansion, and preferably at a known and/or controlled temperature.

In the above description, the grooves 1410, 1420 in the reference bed1400 are arranged in a grid pattern, primarily due to its simplicity andconvenience. However, it will be appreciated that the grooves 1410, 1420in the reference bed 1400 may alternatively be formed with otherpatterns of grooves, so long as the geometry of those patterns is knownwhen performing the detection operation described below.

FIG. 16 illustrates an operation for detecting gantry errorsattributable to the gantry 1010 of the apparatus, according to oneembodiment. In step S1600, an operator installs the reference bed 1400on the apparatus. In one embodiment, the reference bed 1400 temporarilyreplaces the build platen 16 used during normal operation.

In step S1610, the apparatus and the reference bed are warmed up to athreshold temperature range. This step ensures that the reference bedcharacteristics do not deviate from its design due to thermal expansionduring scanning, and ensures the calibration is representative of aprinter while it is printing (as opposed to a cold printer).

In step S1620, the apparatus 1000 performs measurement scans along thesurface of the reference bed using the laser scanner 15. In oneembodiment, the laser scanner 15 performs measurement scans in both Xand Y directions to detect the positions of the reference bed grooves.For instance, to detect the positions along a particular X position ofthe horizontal grooves 1410, the laser scanner 15 may scan along the Ydirection while holding at the particular X position, taking depthmeasurements at intervals along the Y direction. As described below,these depth measurements may be employed to detect the centers of allhorizontal grooves 1410 at the particular X position. The laser scannermay repeat these Y-direction scans at multiple X positions (e.g., atpredetermined intervals along the X direction) to detect the positionsof the horizontal grooves 1410 throughout the entire reference bed 1400.

To detect the positions along a particular Y position of the verticalgrooves 1420, the laser scanner 15 may scan along the X direction whileholding at the particular Y position, taking depth measurements atintervals along the X direction. As described below, these depthmeasurements may be employed to detect the centers of all verticalgrooves 1420 at the particular Y position. The laser scanner may repeatthese X-direction scans at multiple Y positions (e.g., at predeterminedintervals along the Y direction) to detect the positions of the verticalgrooves 1420 throughout the entire reference bed 1400.

In one embodiment, the laser scanner 15 performs the X-direction andY-direction scans using the profile-scanning mode described above, whilecontinuously moving in the respective scan direction to conduct thescan. In one embodiment, the left slope 1500 and the right slope 1510 ofeach groove has a slope sufficiently flat such that the laser scanner 15may accurately profile-scan sample points on the slopes.

In step S1630, the controller 20 determines the locations of centers ofeach reference bed groove for the scan measurement data collected instep S1620. That is, for each Y-direction scan along each X position,the controller 20 determines the center point 1520 of each horizontalgroove 1410 at that X position. And, for each X-direction scan alongeach Y position, the controller 20 determines the center point 1520 ofeach vertical groove 1420 at that Y position. Various known approachesfor analyzing the topologies of the measurement scans may be employedfor this determination, such as algorithms used for surface andtopographical analysis. Alternatively, one novel example of performingstep S1630 that may yield more accurate groove center pointdeterminations is illustrated in FIG. 17 and described in detail below.

In step S1640, the controller 20 computes a regression to represent eachhorizontal groove 1510 and vertical groove 1520. That is, for eachhorizontal groove 1510, the determinations made in step S1630 reveal theY positions of the groove center along the X direction. In the case thatno gantry errors are present, the Y positions for the groove center ofthe horizontal groove 1510 will remain constant along the X direction(i.e., perfectly horizontal). On the other hand, in the case that theX-rails and Y-rails are skewed (i.e., not perfectly aligned at 90degrees), the Y positions for the groove center of the horizontal groove1510 will change along the X direction. The controller 20 computes aregression representing that horizontal groove 1510 from these X and Ypositions of the groove center.

Similarly, for each vertical groove 1520, the determinations made instep S1630 reveal the X positions of the groove center along the Ydirection. In the case that no gantry errors are present, the Xpositions for the groove center of the vertical groove 1520 will remainconstant along the Y direction (i.e., perfectly vertical). On the otherhand, in the case that the X-rails and Y-rails are skewed (i.e., notperfectly aligned at 90 degrees), the X positions for the groove centerof the vertical groove 1520 will change along the Y direction. Thecontroller 20 computes a regression representing that horizontal groove1510 from these X and Y positions of the groove center.

The specific regression employed for this step may depend on the desiredaccuracy. In one embodiment, a linear regression is used for this step.In one embodiment, a higher-order (e.g., polynomial) regression is usedfor this step.

In step S1650, the controller 20 determines the locations ofintersection points between horizontal grooves 1510 and vertical grooves1520, based on the regressions computed in step S1640. In oneembodiment, the controller 20 generates a two-dimensional array of theX-Y locations of intersection points between horizontal grooves 1510 andvertical grooves 1520.

In step S1660, the controller 20 computes, and stores in the memory 21,a transformation representing the positioning offsets between the trueX-Y coordinate system and the measured X-Y coordinate system of thegantry. In one embodiment, the controller 20 determines thetransformation based on deviations between (i) the X-Y locations of thegroove intersections determined in step S1650 and (ii) the expected X-Ylocations of the groove intersections according to the design of thereference bed 1400. In one embodiment, the transformation accounts forone or more types of deviations including translation, scale,shear/skew, and rotation. In one embodiment, the transformation accountsfor global deviations. In one embodiment, the transformation accountsfor both global deviations and localized deviations. It will beappreciated that translation, scale, shear/skew, and rotation aregenerally global deviations, while other deviations (e.g., resultingfrom a bowed axis rail) may be treated as either a series of localizeddeviations or a higher order global deviation.

In one embodiment, the computed transformation is formed as one or moretransformation matrices. In one embodiment, the computed transformationis formed as individual offset amounts corresponding to multiple X-Ylocations distributed across the gantry.

In one embodiment, the above-described gantry error detection operationis performed once for an apparatus during the manufacturing process tocompute the transformation. In one embodiment, the operation isperformed periodically (e.g., during maintenance cycles or at intervalsbetween a number of successive printing operations). In one embodiment,the operation is performed prior to every printing operation.

In one embodiment, a single measurement of the reference bed isperformed. In one embodiment, multiple measurements of the reference bedare performed, and a transformation is generated based on the multiplemeasurements.

FIG. 17 illustrates one example of steps that may be employed to performstep S1630 of determining the locations of the center of each groove.The inventors recognized that determining the precise location of agroove center from depth measurements themselves may be difficult, dueto resolution limitations and noise. For example, the depthmeasurements, by themselves, may not locate an accurate groove centerunless a depth measurement is conducted precisely at the groove centerlocation. Therefore, a need exists to more precisely identify thelocation of the groove center.

In step S1700, the controller 20 distinguishes, at least on a coarsebasis, the areas of the left and right slopes of each V-shaped grooveusing measurements taken along a scan by the laser scanner 15. Forinstance, with reference to FIG. 15, the controller 20 may distinguishthe left slope 1500 based on continually increasing depth measurementsduring a measurement scan moving from left to right. The controller 20may distinguish the right slope 1510 based on subsequent depthmeasurements that begin to decrease after encountering the left slope1500.

In step S1710, the controller 20 isolates the depth measurements fallingwithin the area of the left slope 1500 as distinguished in step S1700(examples illustrated in FIG. 18 as depth measurements 1800), andcomputes a regression representing the left slope 1500 based on thesedepth measurements. The controller 20 also isolates the depthmeasurements falling within the area of the right slope 1510 asdistinguished in step S1700 (examples illustrated in FIG. 18 as depthmeasurements 1810), and computes a regression representing the rightslope 1510. In one embodiment, the computed regressions are linearregressions. In one embodiment, the computed regressions arehigher-order (e.g., polynomial) regressions.

In step S1720, the controller 20 determines the groove center 1520 basedon the intersections of the two regressions computed in step S1710.Using this approach, the groove center 1520 may be accurately determinedeven if that precise location was not subject to a depth measurementduring the measurement scan, and sub-scan resolution positioningaccuracy may be realized.

FIG. 19 illustrates one example of compensating for the gantry errorsafter the detection operation of FIG. 16 has been performed. In stepS1900, the controller 20 receives a set of X-Y coordinates referencingbuild platen position(s). The set of X-Y coordinates may be a single X-Ycoordinate or a plurality of X-Y coordinates.

In step S1910, the controller 20 applies the transformation computed andstored in FIG. 16 (step S1660) to each of the X-Y coordinates in theset. The precise operation to apply the transformation may depend on thenature of the transformation. For example, in the case that thetransformation is formed as one or more transformation matrices, thecontroller 20 may apply these matrices to each X-Y coordinate. In thecase that the transformation is formed as individual stored offsetamounts for X-Y locations distributed across the gantry, the controller20 may apply the offset amount of the X-Y location closest to each X-Ycoordinate in the set. Alternatively, the controller 20 may, for eachX-Y coordinate in the set, interpolate the transformation based on theindividual stored offset amounts and their X-Y locations.

The operation of FIG. 19 may be employed in combination with theoperations described in FIGS. 3 and 11-13. For instance, the operationof FIG. 19 may be performed to transform every X-Y coordinate referencethat arises during the operations in FIGS. 3 and 11-13.

In an alternative embodiment for detecting gantry errors, instead ofperforming the operation once at a threshold temperature range, theoperation of FIG. 16 is performed multiple times while warming up theapparatus 1000 and the reference bed 1400 to multiple differenttemperatures. As a result, individual transformations are computed overmultiple temperatures. To compensate for the gantry errors, theapparatus 1000 may include a temperature sensor to detect the currenttemperature of the apparatus and/or the build platen. The apparatus 1000may then select, among the computed transformations, the one that isclosest to the detected temperature. Alternatively, the apparatus 1000may interpolate a specific transformation based on the detectedtemperature and the plural transformations and correspondingtemperatures.

In yet another embodiment for detecting gantry errors, instead ofperforming step S1610 of warming up the apparatus, the remainingoperation of FIG. 16 is performed while detecting the temperature of theapparatus and/or reference bed using a temperature sensor. To compensatefor the gantry errors, the apparatus 1000 may detect the currenttemperature of the apparatus and/or the build platen, and compute aspecific transformation using the transformation and temperature fromthe detection operation, the detected current temperature, and a knowncoefficient of thermal expansion of the reference bed material.

In still another embodiment for detecting gantry errors, instead ofusing the laser scanner 15, the apparatus 1000 includes an imagingdevice to capture an image of the reference bed 1400 from a plurality ofX-Y positions. The apparatus 1000 performs image analysis to correlateimage changes due to position with expected changes in image position.

In another embodiment, the apparatus 1000 includes encoders (optical ormagnetic) with a high level of accuracy to detect actual changes inposition. This approach may be used, for example, to detect scalingdeviations.

While the above description of the reference bed has been made withrespect to grooves, it will be appreciated that any otherdistinguishable feature may alternatively or additionally be utilized todetect gantry errors without deviating from the invention. For instance,other topographical features, such as projections, may be employedinstead of, or in addition to, grooves.

Backlash Detection and Compensation

Yet another aspect of the invention is an apparatus and method fordetecting and compensating for backlash errors. It will be appreciatedthat this aspect may be used in combination with the above-describedapparatuses and methods of performing 3D-printing and scanning of anobject and the above-described methods of performing gantry errordetection and compensation.

One problem that may arise with scanning movement systems is a phaseshift between scans in the forward direction and scans in the reversedirection. One cause of such phase shift is a phenomenon known asbacklash, which may arise, for example, when components on the head ofthe scanning movement system do not move precisely coincident with oneanother (e.g., due to imprecisions or gaps between components). As aresult, a delay occurs between initiation of a movement source (e.g.,motor) and the actual observed movement in a connected component ofinterest. Backlash may notably occur when movement starts in a differentdirection (e.g., opposite direction) from the previous movementdirection. One example of such a phase shift is illustrated in FIG. 20,which depicts a difference between scanning measurements when performinga forward-direction scan followed by a backward-direction scan along thesame scan path.

Such phase shifts may influence both the measurement and printingoperations described above, resulting in inaccuracies in both thescanning process and the printed object. Therefore, a need exists in theart to detect and compensate for such phase shifts, so that theapparatus may perform accurate measurement and printing operations.

The present invention incorporates an operation for detecting andcompensating for phase shifts caused by backlash. The present inventionalso incorporates an operation for performing bidirectional scanning(scanning in both forward and reverse directions) during depthmeasurements to detect and compensate for phase shifts caused bybacklash.

FIG. 21 illustrates an operation for performing a measurement scan inthe apparatus that detects and compensates for a backlash phase shift,according to one embodiment. In step S2100, the controller 20 receives ascan path representing continual movement of the print head whileperforming measurements (e.g., profile scan or edge scan). The scan pathmay be aligned with the X or Y direction, or may be any path involving acombination of movement in the X and Y directions. The scan pathincludes a start point where the scan is designated to begin, and an endpoint where the scan is designated to end. The direction traversing thescan path from the start point to the end point will be understood as a“forward” direction, while the opposite direction traversing the scanpath from the end point to the start point will be understood as the“reverse” direction. It is noted that the scan path may at least includeany path of movement formed in the scan strategies generated inoperations set forth in FIGS. 3 and 11-13.

In step S2110, the controller 20 updates the scan path, lengthening thescan path at each end to include additional segments to be scanned priorto the start point and additional segments to be scanned beyond the endpoint. The scan segments appended to both ends of the original scan pathallow for truncation in a subsequent step. In one embodiment, thecombined length of the two appended scan segments exceeds the maximumexpected amount of backlash. In one embodiment, the length of eachappended scan segment exceeds the maximum expected amount of backlash.The updated scan path includes an updated start point where the updatedscan is designated to begin, and an updated end point where the updatedscan is designated to end.

In step S2120, the controller 20 causes the laser scanner 15 to performa measurement scan along the updated scan path in the forward direction.That is, the laser scanner 15 takes depth measurements at intervalsalong the updated scan path in the forward direction, starting at theupdated start point until the updated end point, to produce a forwardscan signal.

In step S2130, the controller 20 causes the laser scanner 15 to performa measurement scan along the updated scan path in the reverse direction.That is, the laser scanner 15 takes depth measurements at intervalsalong the updated scan path in the reverse direction, starting at theupdated end point until the updated start point, to produce a reversescan signal. At this point, the forward and reverse scan signals maygenerally correspond to the illustration in FIG. 20, in that a phaseshift exists between these two scan signals.

In step S2140, the controller 20 performs a correlation operationbetween the forward scan signal collected in step S2120 and the reversescan signal collected in step S2130. The correlation operation revealsthe amount of phase shift between the two scan signals. It is understoodthat known correlation methodologies may be employed in this regard.

In step S2150, the controller 20 determines one or more compensationamounts to adjust the scan signals based on the phase shift amountdetermined in step S2140. The controller 20 then applies thecompensation amounts to the scan signals to shift the scan signals toform compensated scan signals that generally coincide with each other.In one embodiment, a compensated amount is determined to be one-half ofthe phase shift amount, such that each scan signal is shifted towardsthe other signal by one-half of the phase shift amount. That is, theforward scan signal is compensated by being shifted in the direction ofthe reverse scan signal by one-half of the phase shift amount.Conversely, the reverse scan signal is compensated by being shifted inthe direction of the forward scan signal by one-half of the phase shiftamount.

In step S2160, the controller 20 generates a final scan signal from oneor both of the scan signals as compensated in step S2150. For example,the controller 20 may generate a final scan signal by selecting one ofthe compensated forward scan signal and the compensated reverse scansignal. Alternatively, the controller 20 may generate a final scansignal by combining the compensated forward and reverse scan signals. Inaddition, the controller 20 may truncate portions of the compensatedforward and reverse scan signals corresponding to scan segments appendedto the original scan path in step S2110.

It will be appreciated that the measurement operation of FIG. 21 may beapplied towards performing any or all of the laser scanner measurementsin the operations of FIGS. 3 and 11-13.

FIG. 22 illustrates an operation for detecting backlash phase shift inthe apparatus, according to another embodiment. In step S2200, anoperator installs the reference bed 1400 (described above with respectto gantry error detection) on the apparatus. In one embodiment, thereference bed 1400 temporarily replaces the build platen 16 used duringnormal operation.

In step S2210, the controller 20 controls the laser scanner 15 toperform a set of bidirectional measurement scans of various scan pathsacross the reference bed 1400 to obtain phase shift amounts forlocations along those scan paths. In one embodiment, the various scanpaths are distributed across the surface of the reference bed 1400 andcover a variety of locations on the reference bed 1400 in a variety ofdifferent directions. This step may employ various above-described stepsfrom the FIG. 21 operation to obtain the phase shift amounts.

In step S2220, the controller 20 stores, in the memory 21, the phaseshift amounts (and/or compensation amounts determined from the phaseshift amounts) corresponding to the various locations and scan pathdirections from step S2210. In one embodiment, the stored informationmay be represented by the illustration in FIG. 23, which depicts ninelocations, each with compensation amounts for eight scan directions. Inparticular, the length of each “lash” extending from a location in aparticular scan direction represents the magnitude of phase shift orcompensation amount. Of course, it will be appreciated that any numberof locations and scan directions may be employed in connection with thisoperation. It will also be appreciated that another object other thanthe reference bed may be used for this operation.

FIG. 24 illustrates an operation for compensating for backlash phaseshift in the apparatus, according to another embodiment. This operationis utilized after the FIG. 22 operation of detecting backlash phaseshift has already been performed. In step S2400, the controller 20receives movement instructions relating to travel of the print head(s)10, 18. The movement instructions may include print instructionsdefining print head travel during production of a print layer, orscanning instructions from a scan strategy defining print head travelfor conducting a measurement scan.

In step S2410, the controller 20 generates compensated movementinstructions based on the stored phase shift amounts or compensationamounts in step S2220. In one embodiment, the compensated movementinstructions are generated by utilizing the compensation amountscorresponding to the closest stored location (and relevant scandirections) to the print head travel. In one embodiment, the compensatedmovement instructions are generated by interpolating the compensationamounts of multiple stored locations (and relevant scan directions). Inthis regard, the compensated movement instructions will counteract thebacklash effects encountered during the print head movement.

The operation of FIG. 24 may be employed in combination with theoperations described in FIGS. 3 and 11-13. For instance, the operationof FIG. 24 may be performed to compensate for backlash during movementof the print head when performing printing, during the operations inFIGS. 3 and 11-13.

In one embodiment, a common compensation amount is applied irrespectiveof location and movement direction. The corresponding operation fordetecting backlash phase shift may involve a bidirectional scan in anyarbitrary location and/or reciprocating direction.

In one embodiment, a compensation amount is applied based on thespecific movement direction, but irrespective of location. Thecorresponding operation for detecting backlash phase shift may involve abidirectional scan in any arbitrary location, performed over a series ofreciprocating directions. For instance, the compensation amount may bedetermined based on a common compensation amount adjusted by a factorthat depends on movement direction.

In one embodiment, a compensation is applied based on the specificlocation, but irrespective of movement direction. The correspondingoperation for detecting backlash phase shift may involve a bidirectionalscan in any arbitrary reciprocating direction, performed over a seriesof locations. For instance, the compensation amount may be determinedbased on a common compensation amount adjusted by a factor that dependson location.

In one embodiment, a compensation is applied based on both the specificlocation and movement direction. The corresponding operation fordetecting backlash phase shift may involve bidirectional scans performedover a series of locations and over a series of reciprocatingdirections. For instance, the compensation amount may be determinedbased on a common compensation amount adjusted by a factor that dependson location and movement direction.

In one embodiment, a compensation is applied based on both the specificmovement direction and the movement speed. The corresponding operationfor detecting backlash phase shift may involve bidirectional scansperformed over a series of reciprocating directions and over a series ofmovement speeds. For instance, the compensation amount may be determinedbased on a common compensation amount adjusted by a factor that dependson movement direction and movement speed.

Incorporation by reference is hereby made to U.S. Pat. Nos. 10,076,876,9,149,988, 9,579,851, 9,694,544, 9,370,896, 9,539,762, 9,186,846,10,000,011, 10,464,131, U.S. Patent Application Publication No.2016/0107379, U.S. Patent Application Publication No. 2018/0154439, U.S.Patent Application Publication No. 2018/0154580, and U.S. PatentApplication Publication No. 2018/0154437 in their entireties.

Although this invention has been described with respect to certainspecific exemplary embodiments, many additional modifications andvariations will be apparent to those skilled in the art in light of thisdisclosure. For instance, while reference has been made to an X-YCartesian coordinate system, it will be appreciated that the aspects ofthe invention may be applicable to other coordinate system types (e.g.,radial). It is, therefore, to be understood that this invention may bepracticed otherwise than as specifically described. Thus, the exemplaryembodiments of the invention should be considered in all respects to beillustrative and not restrictive, and the scope of the invention to bedetermined by any claims supportable by this application and theequivalents thereof, rather than by the foregoing description.

1-18. (canceled)
 19. A method of correcting positioning errors in asystem that includes a movement component, comprising: detecting aplurality of topographical features positioned at different locations onthe surface of an object disposed within the movement system; comparinga location of the detected topographical features to expected locationsfor the topographical features; generating transformation informationbased on the comparison; and correcting movement instructions of themovement component based on the generated transformation information.20. The method of claim 19, wherein the comparing step includes, foreach detected topographical feature: determining the location of thecenter of the respective topographical feature; and comparing thelocation of the center of the respective topographical feature to theexpected location for the topographical feature.
 21. The method of claim19, wherein the comparing step includes, for each detected topographicalfeature: determining a portion of the respective topographical featureas a left-side portion; determining a portion of the respectivetopographical feature as a right-side portion; determining the locationof the center of the respective topographical feature based on thedetermined left-side portion and the determined right-side portion; andcomparing the location of the center of the respective topographicalfeature to the expected location for the topographical feature.
 22. Themethod of claim 21, wherein the location of the center of the respectivetopographical feature is determined based on the intersection of thedetermined left-side portion and the determined right-side portion. 23.The method of claim 21, wherein the location of the center of therespective topographical feature is determined based on the intersectionof a regression performed based on the determined left-side portion anda regression performed based on the determined right-side portion. 24.The method of claim 19, wherein the topographical features includesgrooves.
 25. The method of claim 24, wherein the grooves are V-shaped.26. The method of claim 19, wherein the detecting of the plurality oftopographical features includes detecting the topographical featureswith a laser scanner.
 27. A method of correcting positioning error in a3D-printing system that includes a movement component and a detectioncomponent, comprising: detecting, using the detection component, aplurality of topographical features positioned at different locations ona reference object disposed on the 3D-printing system; comparing alocation of the detected topographical features to expected locationsfor the topographical features; generating transformation informationbased on the comparison; and correcting 3D-printing instructions forcontrolling the movement component, based on the generatedtransformation information.
 28. A method of measuring an object with ameasurement apparatus that includes a measurement component coupled to amovement component, comprising: moving, with the movement component, themeasurement component along a measurement path in a forward direction;detecting, with the measurement component, a forward measurement of theobject along the measurement path during the moving in the forwarddirection; moving, with the movement component, the measurementcomponent along the measurement path in a reverse direction opposite tothe forward direction; detecting, with the measurement component, areverse measurement of the object along the measurement path during themoving in the reverse direction; comparing the forward measurement andthe reverse measurement; and generating a corrected measurement based onthe comparing and at least one of the forward measurement and thereverse measurement.
 29. The method of claim 28, wherein the comparingincludes determining a phase shift between the forward measurement andthe reverse measurement, and wherein the corrected measurement isgenerated based on the phase shift and at least one of the forwardmeasurement and the reverse measurement.
 30. The method of claim 29,wherein the corrected measurement is generated based on the phase shiftand both the forward measurement and the reverse measurement.
 31. Themethod of claim 28, wherein the comparing includes determining a phaseshift between the forward measurement and the reverse measurement, anddetermining a correction shift amount for at least one of the forwardmeasurement and the reverse measurement based on the phase shift, andwherein the corrected measurement is generated based on the at least oneof the forward measurement and the reverse measurement having thecorrection shift amount applied thereto.
 32. The method of claim 28,wherein the comparing includes determining a phase shift between theforward measurement and the reverse measurement, and determining acorrection shift amount for both the forward measurement and the reversemeasurement based on the phase shift, and wherein the correctedmeasurement is generated based on the forward measurement and thereverse measurement having the respective correction shift amountsapplied thereto.
 33. The method of claim 32, wherein the correctedmeasurement is generated based on a combination of the forwardmeasurement and the reverse measurement having the respective correctionshift amounts applied thereto.